This invention relates to interlayer sheet for safety glass assemblies and more particularly to such sheet formed of polyblends of polyvinyl butyral and polyurethane.
Polyvinyl butyral (PVB) sheet is widely used as a clear, transparent, shock-absorbing interlayer in laminated safety glazings for motor vehicle, aircraft, architectural, security (e.g. cashier booths, prison windows, jewelry display cases etc.) and like applications. For example, an automotive windshield containing such interlayer laminated between glass sheets can absorb a blow from an occupant's head without shattering and in doing so dissipates significant impact energy as the windshield undergoes essentially plastic deformation.
When used as interlayer, significant plasticizer is usually present in the PVB and this can limit the service application or, alternatively, dictate the choice of plasticizer when the PVB is adhered to a non-glass surface in a multi-layer laminate. Such special plasticizers, however, usually detract from other desirable laminate properties.
Moreover, it is further known that the optimum level of adhesion of plasticized PVB interlayer to glass (via reaction of residual hydroxyl groups with SiOH groups on the glass surface) occurs at nominal temperatures of about 15.degree.-21.degree. C. and this is why it is preferred in safety glazings. However, glass adhesion (and therefore the energy-absorbing properties of the laminate) appreciably deteriorates on either side of this temperature range e.g., at 0.degree. F. (-17.7.degree. C.) and 120.degree. F. (49.degree. C.).
Furthermore, as designers provide additional sophisticated performance features in safety glazings by incorporating added functional layers, it is necessary to be concerned with adherence of the PVB to such layers to preserve the desired energy-absorption properties.